A conventional combined steel oil control ring typically has a construction that combines steel side rails and a steel spacer expander. The spacer expander includes protruding portions axially extending from the body of the spacer expander like an ear (hereinafter referred to as ear portions) for contacting the side rails. The ear portions are substantially, equally spaced with repect to each other along the internal circumferential portion of the spacer expander. The radially external circumferential surface of the ear portions is adapted to press the side rails radially outwardly by using resilient force caused by the spacer expander. When using such a combined steel oil control ring, the side rails tend to circumferentially rotate relatively to the spacer expander, and, therefore, it is necessary to prevent such rotation from occurring, for achieving the effective performance of the oil control ring. To implement such prevention, an arrangement is proposed in Japanese Utility Model Unexamined Publication Jitsu-Kai-Hei (JP(U)) 1-78768. In the arrangement, the radially external circumferential surfaces of the ear portions contacting the internal circumferential portion of the side rails have contours, each consisting of repeatedly occurring circumferential flat surfaces and neighboring grooves recessed from the flat surfaces (hereinafter referred to as up-and-down contours), formed thereon. The contours are fine, or minute, in this case, like a saw tooth contour, having a tooth pitch of 25-250 μm and a tooth height of 15-180 μm.
The arrangement described in the publication above has a problem in that, because the up-and-down contours on the radially external circumferential surfaces of the ear portions are as fine, the contours easily wear out. When the contours wear out, not only do the side rails tend to circumferentially rotate relatively to the spacer expander, but also the capability of the side rails to follow up the cylinder of the internal combustion engine is caused to deteriorate, which in turn increases consumption of the lubricating oil.
The arrangement described in the publication above also has another problem in that metal molds, or dies, having protruding portions for forming the fine saw-tooth contours on the surfaces of the ear portions easily wear out. This is because each of the protruding portions of the die for forming the fine grooves of the saw tooth contours has a very narrow width as narrow as 12.5-125 μm, which, in turn, causes a deterioration or shortening of the life of the dies .
The present invention is made to solve the occurrence of the above problems in such a conventional combined steel oil control ring, as described above.
An object of the present invention is therefore to provide a combined steel oil control ring having side rails and a spacer expander adapted to press the side rails radially outwardly via ear portions of the spacer expander having up-and-down contours (as defined earlier), each formed along the external surfaces of ear portions of the spacer expander for preventing the side rails from circumferentially rotating relatively to the spacer expander, as described above. The oil control ring prevents wear from occurring in both the up-and-down contours formed on the surface of the ear portions, and in the protruding portions formed on a die for forming the up-and-down contours on the ear portions.